The reaction between a shield and laser is completely random, not knowing wether you are going to vaporise a few molecules, an entire city or everything in between makes it very unreliable for warfare purposes.
And you'd probably find the whole Landsraad against you, as using atomics is outlawed. While a bomb like that isn't an atomic weapon by definition, the effects are the same and it stands to reason that they'll therefore still retaliate in full force.